1. Field of the Invention
The present invention relates to a device for coupling and centering tools with a spindle, for example in a drill for drilling tracks and apparatuses of the track in railway applications.
2. Description of the Related Art
Rotary machine tools usually comprise a spindle on which it is possible to mount or which can form a device for coupling and centering tools, for example drill bits or milling cutters, in order to be able to carry out a certain type of machining on or through them.
Different systems for coupling milling cutters with the spindle are known, including the “Quick” coupling system commonly used in North America and the so-called “Weldon” coupling system used in Europe.
In the known “Weldon” system, the spindle forms a cylindrical coupling seat with two radial tightening dowels (also called “grub screws”) perpendicular to one another and with an annular seal, positioned on the bottom of the coupling seat.
The corresponding tool 1 (FIG. 1), for example a milling cutter, forms a coupling portion 2 able to be inserted in the “Weldon” coupling seat and having a cylindrical outer surface 3 extending from a rear free end 4 of the coupling portion 2 up to a front region thereof 5 from which a work portion 6 of the tool 1 extends. The free end 4 has a beveled radially outer edge that forms an annular sealing surface 8, intended to abut against the annular seal of the “Weldon” coupling seat to prevent leakage of cooling liquid conveyed through the coupling.
In the cylindrical surface 3 two flat locking surfaces 7, 8 are formed locally that are perpendicular to one another and parallel to a longitudinal axis 9 of the tool 1. The locking surfaces 7, 8 are formed in a region spaced from the free end 4 (such as not to interfere with the sealing surface 8) and constitute recesses with respect to the cylindrical surface 3 which determines the maximum radial bulk of the coupling portion 2.
The tool 1 with “Weldon” coupling portion can be locked in the “Weldon” coupling seat through tightening of the two tightening dowels against the locking surfaces 7, 8. The tool 1 of the “Weldon” type also forms a longitudinal hole 10 extending through the entire coupling portion 2 for the passage of the cooling liquid and/or of a centering tip 11.
In the known “Quick” system, the spindle forms a cylindrical coupling seat without annular seal and without radial tightening dowels, but rather with a single tangential pin that interferes with and extends partially through the space delimited by the coupling seat.
The corresponding tool 1′ (FIGS. 2, 3), for example a milling cutter, forms a coupling portion 2′ with a cylindrical outer surface 3′ extending from a rear free end 4′ of the coupling portion 2′ up to a front region thereof 5′ from which a work portion 6 of the tool 1 extends.
In the cylindrical surface 3′ two flat locking surfaces 7′, 8′ are locally formed that are perpendicular to each other and parallel to a longitudinal axis 9′ of the tool 1′. The locking surfaces 7′, 8′ constitute recesses with respect to the cylindrical surface 3 which determines the maximum radial bulk of the coupling portion 2. A first locking surface 7′ of the locking surfaces 7′, 8′ is formed in a region spaced from the free end 4′ whereas a second locking surface 8′ extends up to the free end 4′, making the formation of a sealing surface impossible in this area. In the cylindrical surface 3′ a locking throat 12 is also formed, extending from the second locking surface 8′ in the circumferential direction on an opposite side with respect to the first circumferential surface 7′. Observing in the work direction (forwards) the locking throat extends in the clockwise direction, in other words in the usual direction of rotation of the spindles of machine tools.
In order to prevent the escape of cooling liquid conveyed through the “Quick” coupling, the coupling portion 2′ comprises an annular seal 13, for example an O-ring, received in a circumferential groove 14 formed in the cylindrical surface 3′ distanced from the locking surfaces 7′, 8′ and from the locking throat 12 on an opposite side thereof with respect to the free end 4′.
The coupling portion 2′ of the “Quick” type can be inserted in the “Quick” coupling seat with only one orientation in which the tangential pin is adjacent to and aligned with the second locking surface 8′ and does not interfere with the cylindrical surface 3′. A subsequent rotation of the coupling portion 2′ in the opposite direction to the work rotation direction engages the tangential pin in the locking throat 12 which holds the tool 1′. In the locked position, the annular seal 13 is in abutment against an annular sealing surface of the “Quick” coupling seat.
Thanks to the arrangement of the two locking surfaces 7′, 8′ and to the annular seal 13, the same “Quick” coupling portion can also be used with the “Weldon” coupling seat, whereas the “Weldon” coupling portion cannot be used with the “Quick” coupling seat.
In niche or highly specialized sectors due to the particular work conditions, for example in the field of laying rail tracks, the machine tools (milling cutters, drills) are sometimes special apparatuses, supplied by a few manufacturers and used around the world, whereas an easy and cost-effective purchase of the tools (e.g. the drill bits or the milling cutter bits) from local manufacturers is still impeded by the different coupling standards.